The cryptocurrency has climbed -- with a few sharp dips along the way -- despite a flurry of warnings from top economists and business leaders.

"Bitcoin now seems like a charging train with no brakes," said Shane Chanel, an adviser at investment services firm ASR Wealth Advisers. "There is an unfathomable amount of new participants piling into the cryptocurrency market."

Bitcoin is the most popular cryptocurrency -- a kind of virtual "coin" that is "mined" by computers using complex algorithms.

During its epic rally this year, bitcoin has suffered a series of steep drops, reminding of its extreme volatility. After breaking above $11,000 last week, it abruptly plunged by more than $2,000 before resuming its climb.

Nobel laureate Joseph Stiglitz said last week that bitcoin "ought to be outlawed." But experts inside the industry predict its rally has a lot farther to run.

Bitcoin's rapid rise this year has been powered in part by expectations that established fund managers are set to start pouring money into the virtual currency as it gains legitimacy.

The digital currency has also gotten a big lift this year from mom-and-pop investors in countries like South Korea and Japan who don't want to miss out on the prospect of more big gains.

But a study published this week by Natixis Investment Managers, a major French asset management firm, found that 64% of institutional investors think bitcoin is a bubble.